Lameness of horses is effectively ameliorated with a low volume of mepivacaine administered as a palmar digital nerve block.

Abstract

OBJECTIVE: To determine the effect of 1.5 mL 2% mepivacaine, 0.75 mL 2% mepivacaine, and a combination of 0.75 mL 2% mepivacaine with epinephrine (1:200,000 solution) administered over each palmar digital nerve (PDN) to 6 horses with naturally occurring lameness caused by digital pain. METHODS: In a crossover study design, 6 horses with forefoot-related lameness were randomly assigned to 1 of 3 groups. Each group received, on different study days, a PDN block using 1.5 mL of 2% mepivacaine, 0.75 mL 2% mepivacaine, or 0.75 mL of a combination of 2% mepivacaine and epinephrine (1:200,000 solution) injected over each nerve. The horses' gait while trotting was analyzed with an inertial, sensor-based motion-analysis system immediately before treatment. The assigned treatment was then administered to the lame forelimb, after which the gait was reevaluated at 5-minute intervals for 15 minutes. RESULTS: All 3 treatments significantly reduced lameness scores at all gait evaluations, but the effect of treatment on the lameness score did not differ significantly among treatments. CONCLUSIONS: 0.75 mL of mepivacaine hydrochloric acid injected over each PDN was as effective as twice that volume in decreasing the lameness score of horses with digital pain. The 0.75-mL solution of mepivacaine/epinephrine injected over each nerve did not significantly improve the anesthetic effect of mepivacaine. CLINICAL RELEVANCE: For a palmar digital nerve block, a lower-than-commonly-recommended volume of 2% mepivacaine effectively ameliorates digital pain. This finding invites investigation as to whether administering a low volume of local anesthetic will more precisely localize pain.